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Garching, Germany

The Max-Planck-Institute of Quantum Optics is a part of the Max Planck Society which operates 87 research facilities in Germany.The institute is located in Garching, Germany, which in turn is located 10 km north-east of Munich. Five research groups work in the fields of attosecond physics, laser physics, quantum information theory, laser spectroscopy, quantum dynamics and quantum many body systems. Wikipedia.

Van Den Nest M.,Max Planck Institute of Quantum Optics
New Journal of Physics | Year: 2011

We propose a framework to describe and simulate a class of manybody quantum states. We do so by considering joint eigenspaces of sets of monomial unitary matrices, called here 'M-spaces'; a unitary matrix is monomial if precisely one entry per row and column is nonzero. We show that M-spaces encompass various important state families, such as all Pauli stabilizer states and codes, the Affleck-Kennedy-Lieb-Tasaki (AKLT) model, Kitaev's (Abelian and non-Abelian) anyon models, group coset states, W states and the locally maximally entanglable states. We furthermore show how basic properties of M-spaces can be understood transparently by manipulating their monomial stabilizer groups. In particular, we derive a unified procedure to construct an eigenbasis of any M-space, yielding an explicit formula for each of the eigenstates. We also discuss the computational complexity of M-spaces and show that basic problems, such as estimating local expectation values, are NP-hard. Finally, we prove that a large subclass of M-spaces-containing, in particular, most of the aforementioned examples-can be simulated efficiently classically with a unified method. © IOP Publishing Ltd and Deutsche Physikalische Gesellschaft. Source

Reiserer A.,Technical University of Delft | Rempe G.,Max Planck Institute of Quantum Optics
Reviews of Modern Physics | Year: 2015

Distributed quantum networks will allow users to perform tasks and to interact in ways which are not possible with present-day technology. Their implementation is a key challenge for quantum science and requires the development of stationary quantum nodes that can send and receive as well as store and process quantum information locally. The nodes are connected by quantum channels for flying information carriers, i.e., photons. These channels serve both to directly exchange quantum information between nodes and to distribute entanglement over the whole network. In order to scale such networks to many particles and long distances, an efficient interface between the nodes and the channels is required. This article describes the cavity-based approach to this goal, with an emphasis on experimental systems in which single atoms are trapped in and coupled to optical resonators. Besides being conceptually appealing, this approach is promising for quantum networks on larger scales, as it gives access to long qubit coherence times and high light-matter coupling efficiencies. Thus, it allows one to generate entangled photons on the push of a button, to reversibly map the quantum state of a photon onto an atom, to transfer and teleport quantum states between remote atoms, to entangle distant atoms, to detect optical photons nondestructively, to perform entangling quantum gates between an atom and one or several photons, and even provides a route toward efficient heralded quantum memories for future repeaters. The presented general protocols and the identification of key parameters are applicable to other experimental systems. © 2015 American Physical Society. Source

Tu H.-H.,Max Planck Institute of Quantum Optics
Physical Review B - Condensed Matter and Materials Physics | Year: 2013

We propose a class of projected BCS wave functions and derive their parent spin Hamiltonians. These wave functions can be formulated as infinite matrix product states constructed by chiral correlators of Majorana fermions. In one dimension, the spin Hamiltonians can be viewed as SO(n) generalizations of Haldane-Shastry models. We numerically compute the spin-spin correlation functions and Rényi entropies for n=5 and 6. Together with the results for n=3 and 4, we conclude that these states are critical and their low-energy effective theory is the SO(n)1 Wess-Zumino-Witten model. In two dimensions, we show that the projected BCS states are chiral spin liquids, which support non-Abelian anyons for odd n and Abelian anyons for even n. © 2013 American Physical Society. Source

Romero-Isart O.,Max Planck Institute of Quantum Optics
Physical Review A - Atomic, Molecular, and Optical Physics | Year: 2011

We analyze the requirements to test some of the most paradigmatic collapse models with a protocol that prepares quantum superpositions of massive objects. This consists of coherently expanding the wave function of a ground-state-cooled mechanical resonator, performing a squared position measurement that acts as a double slit, and observing interference after further evolution. The analysis is performed in a general framework and takes into account only unavoidable sources of decoherence: blackbody radiation and scattering of environmental particles. We also discuss the limitations imposed by the experimental implementation of this protocol using cavity quantum optomechanics with levitating dielectric nanospheres. © 2011 American Physical Society. Source

Karshenboim S.G.,Max Planck Institute of Quantum Optics
Physical Review Letters | Year: 2010

Constraint on spin-dependent and spin-independent Yukawa potential at atomic scale is developed. That covers constraints on a coupling constant of an additional photon γ* and a pseudovector boson. The mass range considered is from 1eV/c2 to 1MeV/c2. The strongest constraint on a coupling constant α′ is at the level of a few parts in 1013 (for γ*) and below one part in 1016 (for a pseudovector) corresponding to mass below 1keV/c2. The constraints are derived from low-energy tests of quantum electrodynamics and are based on spectroscopic data on light hydrogenlike atoms and experiments with magnetic moments of leptons and light nuclei. © 2010 The American Physical Society. Source

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